U.S. patent application number 10/493274 was filed with the patent office on 2005-05-19 for spatial scalable compression scheme using spatial sharpness enhancement techniques.
This patent application is currently assigned to Koninklijke Philips Electronics N. V.. Invention is credited to Bruls, Wilhelmus Hendrikus Alfonsus, Dantwala, Nehal R., De Bruijn, Frederik Jan.
Application Number | 20050105814 10/493274 |
Document ID | / |
Family ID | 26077020 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050105814 |
Kind Code |
A1 |
Bruls, Wilhelmus Hendrikus Alfonsus
; et al. |
May 19, 2005 |
Spatial scalable compression scheme using spatial sharpness
enhancement techniques
Abstract
A video encoder/decoder with spatial scalable compression
schemes using spatial sharpness enhancement techniques is
disclosed. The video compression scheme introduces a number of
various video enhancement techniques on the base layer. A picture
analyzer is used to determine the best or the best mix of various
video enhancement techniques. The picture analyzer compares the
selected mix of video enhancement techniques with the original full
resolution input signal to determine for which of the pixels or
groups of pixels a residual enhancement layer is required.
Parameters defining the selected mix of video enhancement
techniques are transmitted to the decoder layer so the same mix of
video enhancement techniques can be used in the decoder layer.
Inventors: |
Bruls, Wilhelmus Hendrikus
Alfonsus; (Eindhoven, NL) ; De Bruijn, Frederik
Jan; (Eindhoven, NL) ; Dantwala, Nehal R.;
(Redmond, WA) |
Correspondence
Address: |
Corporate Patent Counsel
Philips Electronics North America Corporation
PO Box 3001
Briarcliff Manor
NY
10510
US
|
Assignee: |
Koninklijke Philips Electronics N.
V.
Groenewoudseweg 1
NL-5621 BA Eindhoven
NL
|
Family ID: |
26077020 |
Appl. No.: |
10/493274 |
Filed: |
April 21, 2004 |
PCT Filed: |
October 16, 2002 |
PCT NO: |
PCT/IB02/04298 |
Current U.S.
Class: |
382/240 ;
375/E7.09; 375/E7.092; 375/E7.124; 375/E7.13; 375/E7.134;
375/E7.137; 375/E7.139; 375/E7.153; 375/E7.155; 375/E7.178;
375/E7.181; 375/E7.186; 375/E7.211; 375/E7.219; 375/E7.233;
375/E7.25; 375/E7.254; 382/239 |
Current CPC
Class: |
H04N 19/12 20141101;
H04N 19/182 20141101; H04N 19/33 20141101; H04N 19/147 20141101;
H04N 19/517 20141101; H04N 19/132 20141101; H04N 19/115 20141101;
H04N 19/124 20141101; H04N 19/172 20141101; H04N 19/187 20141101;
H04N 19/61 20141101; H04N 19/577 20141101; H04N 19/587 20141101;
H04N 19/192 20141101 |
Class at
Publication: |
382/240 ;
382/239 |
International
Class: |
G06K 009/36 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2001 |
EP |
01204066.3 |
Mar 8, 2002 |
EP |
02075917.1 |
Claims
1. A layered encoder for encoding an input video bitstream, the
encoder comprising: a layered encoder unit for encoding a base
bitstream at a lower resolution and a residual bitstream, the
layered encoder unit comprising: a number of enhancement units,
each with a different enhancement algorithm for enhancing a decoded
upscaled base stream and outputting enhanced base video streams; a
picture analyzer for comparing the input video bitstream with the
decoded upscaled base bitstream and the enhanced base video
streams, where the output of the picture analyzer controls the
information included in the residual bitstream.
2. The layered encoder according to claim 1, wherein the picture
analyzer selects a vector representing mix parameters for
calculating the mixture of the enhanced base video streams and
controls the information in the residual bitstream using the
selected vector.
3. The layered encoder according to claim 2, wherein the picture
analyzer compares the selected mixture of enhanced base video
streams with the input video bitstream to determine for which
pixels or group of pixels additional enhancement is required via
the residual bitstream.
4. The layered encoder according to claim 2, wherein each group of
pixels is enhanced using different vectors.
5. The layered encoder according to claim 2, wherein the picture
analyzer calculates a cost function for a limited number of test
vectors and the test vector with the lowest cost function is
selected.
6. The layered encoder according to claim 5, wherein the selected
vector is included in a compressed data stream.
7. The layered encoder according to claim 5, wherein a number of
the test vectors are already selected vectors of neighboring, in
time and space, group of pixels.
8. The layered encoder according to claim 1, wherein the layered
encoding unit further comprises: a downsampling unit for reducing
the resolution of the input video bitstream; a base encoder for
encoding the lower resolution base stream; an upscaling unit for
decoding and increasing the resolution of the base stream to
produce an upscaled base bitstream; a subtraction unit for
subtracting the upscaled base bitstream from the input video
bitstream to produce the residual bitstream; switching means for
selectively allowing only portions of the residual bitstream to be
sent to an enhancement encoder based upon a control signal from the
picture analyzer; the enhancement encoder for encoding the portions
of the residual bitstream which pass through the switching means to
form the encoded residual bitstream.
9. The layered encoder according to claim 8, wherein said switching
means is a multiplier having a value between 0 and 1, wherein a
value of 0 means the switching means is open and a value of 1 means
the switching means is closed.
10. A layered decoder unit for decoding a base bitstream and a
residual bitstream, the layered decoder unit comprising: means for
enhancing the decoded base bitstream, the means for enhancing
comprising a plurality of enhancement units having different
enhancement algorithms for outputting an enhanced base video
stream, and means for superimposing the decoded residual bitstream
on the enhanced base video stream.
11. A layered decoder unit as claimed in claim 10, wherein the
decoder is arranged to receive a vector representing mix parameters
for calculating the mixture of enhanced base streams produced by
the plurality of enhancement units in order to produce the enhanced
base video stream.
12. A method for encoding an input video bitstream the method
comprising the steps of: encoding a base bitstream and a residual
bitstream, comprising the steps of: enhancing a decoded upscaled
base bitstream in a plurality of different enhancement algorithms
outputting enhanced base video streams; comparing the input video
bitstream with the decoded upscaled base bitstream and the enhanced
base video streams, where the output of the comparision controls
the information contained in the residual bitstream.
13. The method according to claim 12, wherein a vector representing
mix parameters for calculating a mixture of the enhanced base video
streams is selected controls the information in the residual
bitstream using the selected vector.
14. The method according to claim 13, wherein the selected mixture
of enhanced base video streams is compared with the input video
bitstream to determine for which pixels or group of pixels
additional enhancement is required via the residual bitstream.
15. The method according to claim 13, wherein each group of pixels
is enhanced using different vectors.
16. The method according to claim 13, wherein a cost function for a
limited number of test vectors is calculated and the test vector
with the lowest cost function is selected.
17. The method according to claim 16, wherein the selected vector
is included in a compressed data stream.
18. The method according to claim 16, wherein a number of the test
vectors are already selected vectors of neighboring, in time and
space, group of pixels.
19. The method according to claim 12, further comprising the steps
of: reducing the resolution of the input video bitstream; encoding
the lower resolution base stream; decoding and increasing the
resolution of the base stream to produce an upscaled base
bitstream; subtracting the upscaled base bitstream from the input
video bitstream to produce the residual bitstream; selectively
allowing only portions of the residual bitstream to be sent to an
enhancement encoder based upon a control signal from the picture
analyzer; encoding the selectively allowed portions of the residual
bitstream to form the encoded residual bitstream.
20. A method of decoding a base bitstream and a residual bitstream,
the decoding comprising: enhancing the decoded base bitstream in a
plurality of different enhancement algorithms for outputting an
enhanced base video stream, and superimposing the decoded residual
bitstream on the enhanced base video stream.
21. A method of decoding as claimed in claim 20, wherein the method
further comprises receiving a vector representing mix parameters
for calculating the mixture of enhanced base streams produced by
the plurality of enhancement units in order to produce the enhanced
base video stream.
22. A compressed data stream including: a base bitstream and a
residual bitstream, wherein the information included in the
residual bitstream represents a difference between a bitstream at
higher resolution than the base bitstream and an enhanced decoded
upscaled base bistream, which enhanced decoded upscaled base
bitstream is based on the base bitstream and wherein the
enhancement has been performed by a mixture of a plurality of
enhancement algorithms.
23. A compressed data stream as claimed in claim 22, wherein the
compressed data stream includes a vector representing mix
parameters for calculating the mixture.
24. A storage medium on which a compressed data stream as claimed
in claim 22 has been stored.
25. A layered encoder/decoder for encoding and decoding an input
video bitstream, comprising: a layered encoder unit for encoding a
base bitstream at a lower resolution and a residual bitstream, the
layered encoder unit comprising: a number of enhancement units,
each with a different enhancement algorithm for enhancing a decoded
upscaled base stream and outputting enhanced base video streams; a
picture analyzer for comparing the input video bitstream with the
decoded upscaled base bitstream and the enhanced base video
streams, where the output of the picture analyzer controls the
information contained in the residual bitstream; a layered decoder
unit for decoding the base bitstream and the residual bitstream,
the layer decoder unit comprising: means for performing the same
enhancement to the decoded base bitstream as was performed in the
encoder unit; and means for superimposing the decoded residual
bitstream on the decoded and enhanced video base stream to produce
a video output stream.
26. A computer program product comprising software code portions
for performing the steps of claim 12 when said product is run on a
computer.
27. A computer program product comprising software code portions
for performing the steps of claim 20 when said product is run on a
computer.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a video encoder/decoder, and more
particularly to a video encoder/decoder with spatial scalable
compression schemes using spatial sharpness enhancement
techniques.
BACKGROUND OF THE INVENTION
[0002] Because of the massive amounts of data inherent in digital
video, the transmission of full-motion, high-definition digital
video signals is a significant problem in the development of
high-definition television. More particularly, each digital image
frame is a still image formed from an array of pixels according to
the display resolution of a particular system. As a result, the
amounts of raw digital information included in high-resolution
video sequences are massive. In order to reduce the amount of data
that must be sent, compression schemes are used to compress the
data. Various video compression standards or processes have been
established, including, MPEG-2, MPEG-4, and H.263.
[0003] Many applications are enabled where video is available at
various resolutions and/or qualities in one stream. Methods to
accomplish this are loosely referred to as scalability techniques.
There are three axes on which one can deploy scalability. The first
is scalability on the time axis, often referred to as temporal
scalability. Secondly, there is scalability on the quality axis,
often referred to as signal-to-noise scalability or fine-grain
scalability. The third axis is the resolution axis (number of
pixels in image) often referred to as spatial scalability or
layered coding. In layered coding, the bitstream is divided into
two or more bitstreams, or layers. Each layer can be combined to
form a single high quality signal. For example, the base layer may
provide a lower quality video signal, while the enhancement layer
provides additional information that can enhance the base layer
image.
[0004] In particular, spatial scalability can provide compatibility
between different video standards or decoder capabilities. With
spatial scalability, the base layer video may have a lower
resolution than the input video sequence, in which case the
enhancement layer carries information which can restore the
resolution of the base layer to the input sequence level.
[0005] FIG. 1 illustrates a known layered video encoder 100. The
depicted encoding system 100 accomplishes layer compression,
whereby a portion of the channel is used for providing a low
resolution base layer and the remaining portion is used for
transmitting edge enhancement information, whereby the two signals
may be recombined to bring the system up to high-resolution. The
high resolution video input is split by splitter 102 whereby the
data is sent to a low pass filter 104 and a subtraction circuit
106. The low pass filter 104 reduces the resolution of the video
data, which is then fed to a base encoder 108. In general, low pass
filters and encoders are well known in the art and are not
described in detail herein for purposes of simplicity. The encoder
108 produces a lower resolution base stream which is provided to a
second splitter 110 from where it is output from the system 100.
The base stream can be broadcast, received and via a decoder,
displayed as is, although the base stream does not provide a
resolution which would be considered as high-definition.
[0006] The other output of the splitter 110 is fed to a decoder 112
within the system 100. From there, the decoded signal is fed into
an interpolate and upsample circuit 114. In general, the
interpolate and upsample circuit 114 reconstructs the filtered out
resolution from the decoded video stream and provides a video data
stream having the same resolution as the high-resolution input.
However, because of the filtering and the losses resulting from the
encoding and decoding, certain errors are present in the
reconstructed stream. These errors are determined in the
subtraction circuit 106 by subtracting the reconstructed
high-resolution stream from the original, unmodified
high-resolution stream. The output of the subtraction circuit 106
is fed to an enhancement encoder 116 which outputs a reasonable
quality enhancement stream.
[0007] The disadvantage of filtering and downscaling the input
video to a lower resolution and then compressing it is that the
video loses sharpness. This can to a certain degree be compensated
for by using sharpness enhancement after the decoder. Although this
can be made to work reasonably well for most parts of the video
picture, there are some areas within the picture where the result
remains poor compared to the original picture, e.g., small text
parts will remain unreadable even with the most sophisticated
enhancement.
SUMMARY OF THE INVENTION
[0008] The invention overcomes the deficiencies of other known
layered compression schemes by increasing the video compression of
a scalable compression scheme by the introduction of a number of
video enhancement techniques on the base layer. Using a video
picture analyzer, the best mix of the various video enhancement
techniques is determined and parameters defining this mix are
transmitted to the decoder section as user data. The video picture
analyzer compares the selected mix of enhanced bitstreams with the
original full resolution input signal and determines for which
pixels a residual enhancement layer is required.
[0009] According to one embodiment of the invention, a method and
apparatus for encoding and decoding an input video bitstream is
disclosed. A base bitstream and a residual bitstream are encoded in
the following manner. A decoded upscaled base bitstream is enhanced
in a first plurality of enhancement units having different
enhancement algorithms and a plurality of enhanced base video
streams are outputted. The input video bitstream is compared with
the decoded upscaled base bitstream and the enhanced base video
streams, where the output of the picture analyzer controls the
information contained in the residual bitstream. The base bitstream
and the residual bitstream are decoded in the following manner. The
same enhancement is performed on the decoded base bitstream as was
performed in the encoder unit. The decoded residual bitstream is
superimposed on the decoded and enhanced base video stream to
produce a video output bitstream.
[0010] According to another embodiment of the invention, a mix of
the enhanced base video streams and the decoded upscaled base
bitstream can be used to control the information in the encoded
residual bitstream, i.e., which pixels or groups of pixels should
be included in the decoded residual bitstream.
[0011] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described, by way of example, with
reference to the accompanying drawings, wherein:
[0013] FIG. 1 is a block diagram representing a known layered video
encoder;
[0014] FIG. 2 is a block diagram of a layered video encoder/decoder
according to one embodiment of the invention;
[0015] FIG. 3 is a block diagram of a layered video encoder/decoder
according to one embodiment of the invention; and
[0016] FIG. 4 is an illustration of a vector candidate set location
according to one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] According to one embodiment of the invention, a spatial
scalable compression scheme using spatial sharpness enhancement
techniques is disclosed. Briefly, the filtered and downscaled video
sequence is compressed. Then, out of the decoded base layer frames,
several upscaled versions are processed using a variety of
enhancement algorithms. This can include a standard upscaled and
filtered, for example, nyquist filtered, versions as well as
various sharpness enhancement algorithm versions. A picture
analyzer processes all of the information and selects the best or
the best mix of these versions. The mix parameters which define the
selected mix is also inserted in the encoded residual bitstream, as
user data, so that the decoder can exactly reproduce this
enhancement.
[0018] However, in some areas of the sharpness enhanced frames, the
results will remain inadequate. By comparing in the encoder the
available original full resolution frames with the enhancement
frames, these areas can be detected. Only these detected areas will
be compressed and be part of the residual bitstream which is
inputted into the enhancement layer. The decoder then decodes the
base layer downscaled bitstream and applies the same enhancement
parameters on the decoded output as was performed in the encoder.
The decoder then decodes the residual bitstream and superimposes
the decoded bitstream on the pixels of the already decoded and
enhanced base layer frames.
[0019] This embodiment will now be described in more detail with
reference to FIG. 2 which is a block diagram of an encoder/decoder
which can be used with the invention. The depicted
encoding/decoding system 200 accomplishes layer compression,
whereby a portion of the channel is used for providing a low
resolution base layer and the remaining portion is used for
transmitting edge enhancement information, whereby the two signals
may be recombined to bring the system up to high-resolution. The
high resolution video input 201 is split by a splitter 210 whereby
the data is sent to a low pass filter 212, for example a nyquist
filter, and a splitter 232. The low pass filter 210 reduces the
resolution of the video data, which is then fed to a base encoder
214. In general, low pass filters and encoders are well known in
the art and are not described in detail herein for purposes of
simplicity. The base encoder 214 produces a lower resolution base
stream 215. The base stream can be broadcasted, received and via a
decoder, displayed as is, although the base stream does not provide
a resolution which would be considered as high-definition.
[0020] The encoder also outputs a decoded base stream to an
upscaling circuit 216. In addition, a decoder (not illustrated) can
be inserted into the circuit after the encoder 214 to decode the
output of the encoder prior to being sent to the upscaling circuit
216. In general, the upscaling circuit 216 reconstructs the
filtered out resolution from the decoded video stream and provides
a video data stream having the same resolution as the
high-resolution input. The upscaled bitstream v1 from the upscaling
circuit 216 is split by a splitter 218 and inputted into a picture
analyzer 230, a subtraction circuit 234 and a splitter 220. The
upscaled bitstream v1 from splitter 220 is inputted into
enhancement units 222 and 224. Each enhancement unit operates a
different spatial enhancement algorithm which will be explained in
more detail below. FIG. 2 has two enhancement units but it will be
understood that any number of enhancement units can be used in the
invention.
[0021] Many video enhancement techniques exist and they all modify
the picture content such that the appreciation of the resulting
picture is improved. The subjective characteristic of these
enhancements complicate the optimization process and is likely the
reason for the diversity in video enhancement algorithms. Various
enhancement algorithms contribute by some means to the picture
quality, and as a result, they often appear in a chain to profit
from the individual strengths. Noise reduction and sharpness
improvement algorithms are just a few examples out of a large set
of enhancement algorithms. It will be understood that any of these
known enhancement algorithms can be used in the invention.
[0022] A high-quality spatial enhancement function consists of a
collection of algorithms that contribute to different aspects of
sharpness. Some algorithms only improve the gradients in the
picture by increasing its steepness, whereas others modify the
amplitude of the gradients. It may seem that these algorithms are
mutually exclusive, however, this is far from true. Both means to
improve the gradient characteristics may be used, where a
predefined model determines the individual contribution of each
algorithm.
[0023] Returning to FIG. 2, the upscaled bitstreams v1 are
processed in enhancement units 222 and 224 according to the
enhancement algorithms in each unit. The resulting video streams
from enhancement units 222 and 224 are inputted into subtraction
units 226 and 228 respectively, wherein the bitstream v1 is
subtracted from the resulting video streams from enhancement units
222 and 224 to produce video streams v2 and v3, respectively. Video
streams v2 and v3 are inputted into the picture analyzer 230. The
input bitstream 201 is also inputted into the picture analyzer 230
via splitter 232. The picture analyzer 230 compares v1, v2 and v3
with the original bitstream and determines how best to enhance the
picture. The picture analysis performed by the picture analyzer can
be performed in a variety of ways. For example, the picture
analyzer 230 could compare v1, v2 and v3 with the original picture
and select the video stream (v1, v2 or v3) which best approximates
the original picture. Alternatively, the picture analyzer can use a
mix of the different bitstreams using mix parameters (.alpha.,
.beta.) or enhancement vectors such that the optimum overall
picture quality is achieved from a combination of video streams.
For example, the picture analyzer can select a vector representing
the mix parameters for calculating the mixture of the enhanced base
video streams to control the information in the residual bitstream
using the selected vector. Furthermore, bit cost function can also
be used in determining the best mix parameters as will be explained
below with reference to FIG. 3. It will be understood that other
schemes than the ones described can be used in the picture analyzer
230 and the invention is not limited thereto.
[0024] There are numerous advantages to using mix parameters in the
picture analyzer 230. Firstly, this is a completely expandable
system. If there are more functions to contribute to the sharpness
of the picture, they can be easily accounted for. The new functions
need not be optimized for the system. Secondly, the
interdependencies of various functions can be accounted for while
deciding on the suitable enhancement vectors. Thirdly, a
spatio-temporal consistency model can be incorporated in the
picture analyzer 230.
[0025] The upscaled output of the upscaling circuit 216 is
subtracted from the original input 201 in a subtraction circuit 234
to produce a residual bitstream which is applied to a switch 236.
The switch is controlled by the output of the picture analyzer 230.
By comparing the input video bitstream 201 with the various
enhanced base video streams, the picture analyzer 230 can determine
which pixels or groups of pixels (blocks) need to be further
enhanced by the enhancement layer 208. For the pixels or groups of
pixels (blocks) that are determined to need enhancement by the
picture analyzer 230, the picture analyzer 230 outputs a control
signal to close switch 236 to let those parts of the residual
bitstream through to the enhancement layer encoder 240. The picture
analyzer 230 also sends the selected mix parameters and the control
signal for the switch to the encoder 240 so that this information
is encoded with the resulting residual bitstream from switch 236
and outputted as the enhancement stream 241.
[0026] The base stream 215 is sent to a base decoder 250 and the
enhancement stream 241 is sent to an enhancement encoder 252 in the
decoder section 204. The decoder 250 decodes the base stream 215
which is then upscaled by an upscaling circuit 254. The upscaled
decoded bitstream is then split by a splitter 256 and sent to
enhancement units 262 and 264, merge unit 270 and addition unit
272. Enhancement unit 262 comprises the same spatial enhancement
algorithm as enhancement unit 222 and enhancement unit 264
comprises the same spatial enhancement algorithm as enhancement
unit 224. The enhancement units 262 and 264 perform their
respective algorithms and send outputs v2 and v3 to the merge unit
270.
[0027] The enhancement decoder 252 decodes the enhancement stream
and outputs the residual bitstream to the addition unit 272. In
addition, the decoder 252 decodes the mix parameters and control
signal and send this information to the merge unit 270. The merge
unit merges together all of the inputs to create the enhancement
output from the picture analyzer 230. The upscaled decoded base
stream and the decoded residual bitstream are combined together by
the addition unit 272 and the resulting bitstream is applied to the
switch 274. The switch 274 is controlled by the control signal so
that the output of the merge unit 270 can be applied to the
appropriate pixels or blocks in the bitstream outputted by the
addition unit 272 so as to produce the output signal 276.
[0028] FIG. 3 is a block diagram of an encoder/decoder 300
according to another embodiment of the invention. Many of the
components in FIG. 3 are the same as the components illustrated in
FIG. 2 so they have been given the same reference numerals. In
addition, for the sake of brevity, the operations of the similar
components will not be described. In this embodiment, a cost
function is used in determining the mix parameters .alpha., .beta.,
. . . for the individual enhancement signals v2, v3, . . . .
According to one embodiment of the invention, enhancement vectors
are assigned on a block by block basis. Previously determined best
enhancement vectors from a spatio-temporal neighborhood are
evaluated in a cost function as illustrated in FIG. 4. The cost
function calculates a metric that is related to the objective
picture quality. The best estimate of the enhancement vector is
defined by one yielding the smallest cost, i.e., Best vector=min
e(.alpha..sub.i, .beta..sub.i, . . . ) where i=1, 2, . . . number
of candidates and e() is the cost function with vectors
.alpha..sub.i, .beta..sub.i, . . . as parameters.
[0029] The cost function should incorporate within itself all the
factors that define good quality and also artifact prevention
mechanism. For example, in case of sharpness enhancement function,
the steepness of the gradients is an important factor and should be
accounted for in the cost function. Artifacts like aliasing that
result from sharpness improvement should also be included in the
cost function. The cost function serves as a quality measure.
[0030] Returning to FIG. 3, the enhancement layer encoder 240 sends
bitcost information to the picture analyzer 230. The cost function
is calculated from the mixed signal Ve(.alpha.,.beta., . . . ) for
a limited set of parameters .alpha.,.beta., . . . . The better the
picture quality of the signal Ve(.alpha.,.beta., . . . ), the lower
the cost function becomes. For every pixel or group of pixels a few
vectors of can be tested. The test vector with the lowest cost
function is then selected. In one embodiment, some of the test
vectors are already selected vectors of neighboring, in time and
space (previous frame), group of pixels. For example, vectors
.lambda..sub.1.beta..sub.1, .lambda..sub.2.beta..sub.2,
.lambda..sub.3.beta..sub.3 illustrated in FIG. 4 are neighbors of
the group of pixels being tested. In addition one or more vectors
can be selected with a random offset. The picture analyzer outputs
Ve=v1+.alpha.v2+.beta.v3 and Vb=v1+.lambda.v2+.mu.v3 where .alpha.,
.beta. are the mix parameters and .lambda., .mu. are the cost
function parameters. In this embodiment, the signal Vb is
subtracted from the original input bitstream in the subtractor 234
to form the residual bitstream. Whenever the final cost function
exceeds a predetermined threshold limit, the picture analyzer
outputs a signal s to the switch 236 so that the switch will close
and for that group of pixels a residual bitstream is encoded in the
encoder 240. In addition, the picture analyzer also sends the
control signal, the mix parameters and the cost function to the
encoder 240 which are then coded and inserted into the enhancement
stream 241. When the enhancement stream is decoded in the
enhancement decoder 252, the mix parameters and cost function are
decoded and sent to the merge unit 270. The merge unit outputs Vb
which is added to the decoded enhancement stream in the addition
unit 272 and the resulting bitstream is applied to the switch 274.
The switch 274 is controlled by the control signal S so that Ve
from the merge unit 270 can be applied to the appropriate pixels or
blocks in the bitstream outputted by the addition unit 272 so as to
produce the output signal 276.
[0031] The above-described embodiments of the invention enhance the
efficiency of spatial scalable compression by using a picture
analyzer to select the best or a mix of a plurality of enhanced
base bitstreams via determined enhancement vectors to control the
information in the encoded residual bitstream. It will be
understood that the different embodiments of the invention are not
limited to the exact order of the above-described steps as the
timing of some steps can be interchanged without affecting the
overall operation of the invention. Furthermore, the term
"comprising" does not exclude other elements or steps, the terms
"a" and "an" do not exclude a plurality and a single processor or
other unit may fulfill the functions of several of the units or
circuits recited in the claims.
* * * * *